1. Technical Field
This invention relates to a continuous process for separating organic compounds from water.
2. Description of the Prior Art
The chemical process industry for some time now has been researching and developing chemical engineering processes for the removal of synthetic organic compounds from the environment. Typically, these artificially produced organic compounds have been identified as potentially toxic to man either directly or indirectly through the food chain. Examples include polychlorinated biphenols (PCBs), chlorodiphenols, Aroclors.RTM., Kanechlors.RTM., and their cogeners.
PCBs were first synthesized over 100 years ago. Under standard conditions, they exist as heavy liquids weighing from about 1.2 to 1.4 kilograms per liter in the form of a slightly viscous oil to a sticky resin. PCBs are derivatives of the compound biphenol in which 1 to 10 hydrogen atoms have been replaced with chlorine atoms. PCBs are fire resistant and have high boiling points. PCBs have extremely high chemical and thermal stability and are quite useful in commercial applications such as dielectric fluids for capacitors and transformers, as heat transfer and hydraulic fluids, pigments, plasticizers, fluids for carbonless copying paper and electromagnets, and as components in cutting oils.
PCBs were widely used in the last 50 years. A lack of recognition of the hazards led to their wide distribution in the environment. Although the United States Environmental Protection Agency has labeled PCBs as having fairly low acute toxicities, some adverse effects have been found in humans, laboratory animals, and other organisms. There is some evidence that PCBs bioaccumulate and may be carcinogenic. Concern over the PCB contamination problem has led to toxic substances control legislation that will require the eventual elimination of the use of PCBs in the United States.
Separation and removal from water of PCBs in very low levels, i.e., part per billion levels, is a complex and expensive task. PCBs are colorless, odorless, and relatively insoluble in water. The Industrial Environmental Research Laboratory of the U.S. Environmental Protection Agency has specified the solubility of PCBs in water to be in the range of 0.007-5.9 mg/l or 7-5900 parts per billion (ppb). This solubility level indicates that physical separation techniques most likely would be unsuccessful in separating PCB from waste water to below 7-5900 ppb, and that a chemical separation process would be the technique of choice for achieving lower PCB levels.
Conventional chemical engineering practice employs a carbon adsorption process for removing chlorinated hydrocarbons, including PCBs, from an aqueous waste stream. The waste water is passed through a vessel filled with activated carbon in the form of carbon slurry or granules. Impurities from the aqueous stream are removed by adsorption onto the carbon. Activated carbon has an affinity for organics and is commonly used on a commercial scale for organic contaminant removal from waste water. However, activated carbon adsorption of PCBs has a major drawback in that it requires the disposal or regeneration of the carbon adsorbor.
Other conventional physical/chemical separation processes are used to remove PCBs from waste water. Sedimentation, coagulation, and flocculation are examples of conventional physical or chemical separation process which can be used for PCB removal from waste water. According to O'Brien and Gere Engineers, Inc., conventional techniques can remove 50 to 80% of the PCBs at influent levels in the range of 1 to 20 micrograms per liter. The New York State Department of Environmental Conservation has also concluded that these conventional techniques can remove 50 to 80% of the PCBs at influent levels in the range of 1 to 10 micrograms per liter and that 90% removal via a coagulation/filtration process represents the highest reduction consistently achievable in existing plants. While higher removals may be theoretically possible, the degree of control required for these removals and the normal variations in the quality of surface waters combine to set 90% removal as a practical limit.
Governmental regulatory agencies at the federal and state levels have mandated a reduction in PCB content in waste waters to levels less than 1 ppb. Reductions in other synthetic chemicals, such as dioxin, similarly have been proscribed to levels below that detectable by conventional analytical techniques.
Even though PCBs, dioxins, or other regulated organic substances have not been used for many years in a particular industrial facility, these substances have been observed in the discharges even after substantial cleanup programs have been carried out. A process is needed to clean up low level amounts of these contaminants in waste water discharged from most industrial facilities.
It is an object of the present invention to provide a continuous process for removing slightly soluble synthetic organic compounds from water.
It is another object to provide a continuous process for removing organic compounds from waste water while eliminating the disposal or regeneration problems associated with contaminated filter media.
It is a further object to provide a continuous process for removing organic compounds in low level amounts from waste water in a cost-efficient manner.